1. Field of the Invention
The present invention relates to an oxygen ion conductor device including two electrode thin films and an oxygen ion conductive thin film interposed between the two electrode thin films, a method for fabricating the oxygen ion conductor device and an oxygen concentration control system using the oxygen ion conductor device.
2. Description of the Prior Art
Conventionally, oxygen concentration control systems for separating oxygen in a target air using an oxygen ion conductor device have been known. An oxygen ion conductor device used for such an oxygen concentration control system includes, for example, a solid electrolyte having oxygen ion conductivity and first and second electrode films disposed on both of surfaces of the solid electrolyte, respectively. When a DC voltage is applied to each of the electrode films to generate a potential difference between the electrode films, electrons are given to oxygen absorbed to a negative electrode film of the two electrode films. The oxygen is converted into oxygen ions. The oxygen ions move in the solid electrolyte to reach the other electrode film, i.e., a positive electrode film. Then, electrons are taken away by the positive electrode film and the oxygen ions are again converted into oxygen. In this manner, the oxygen concentration control system utilizes the oxygen ion conductivity of the oxygen ion conductor device to selectively separate oxygen from a target atmosphere, thereby reducing, for example, the oxygen concentration of inside of a refrigerator.
In the oxygen concentration control system, to improve a separation rate of oxygen in a target space, an oxygen ion conductor film is sometimes used as the solid electrolyte. Specifically, as shown in FIG. 10, the oxygen concentration control system includes a porous supporting substrate 103 at an opening of a wall surface 101 of a deoxygenated storage. On a surface of the supporting substrate 103 (i.e., a lower surface thereof in FIG. 10), an oxygen ion conductor device 102 including stacked layers, i.e., a first electrode thin film 104, an oxygen ion conductor device thin film 106 and a second electrode thin film 105 is provided. Moreover, the oxygen concentration control system further includes an ion-conduction driving power supply 107 for applying a voltage to the electrode films 104 and 105 and a heater 108 for heating the oxygen ion conductive thin film 106 to improve oxygen ion conductivity of the oxygen ion conductive thin film 106. The heater 108 is provided on an upper surface of the supporting substrate 103 with a spacer 110 interposed therebetween. Furthermore, a heater driving power source 109 is connected to the heater 108.
In the above-described structure, when the ion-conduction power source 107 and the heater power source 109 are energized, oxygen 111 in a target air in the deoxygenated storage is converted into oxygen ions in the second electrode thin film 105 and the oxygen ions move in the oxygen ion conductive thin film 106. In this case, the oxygen ion conductive thin film 106 is heated through the supporting substrate 103 and the spacer 110 by the heater 108, so that the oxygen ion conductivity of the oxygen ion conductive thin film 106 is increased. Therefore, oxygen ions moving in the oxygen ion conductive thin film 106 speedily reach the first electrode thin film 104 and are again converted into the oxygen 111. Thus, the oxygen 111 separated by the oxygen ion conductor device 102 passes through the porous supporting substrate 103 and then released to the outside of the deoxygenated storage (See Japanese Laid-Open Publication No. 9-241003).
The oxygen ion conductor device 102 is formed by forming the first electrode thin film 104, the oxygen ion conductive thin film 106 and the second electrode thin film 105 are formed in this order on a surface (a lower surface in FIG. 10) of the porous supporting substrate 103 of alumina by sputtering. Unless the supporting substrate 103 is porous, oxygen does not pass therethrough. Therefore, it is required that the supporting substrate 103 is porous.